Fun-tac, fun-tack, BlueStic, museum puddy all are used to stick stuff. Usually papers to walls. But some grades of the museum stuff is used to mount something valuable that you will have to wrestle with to steal off its display stand, even comes in clear. Might be useful in making a knife display.
I noticed that Locktite and Dap both make the blue stuff. I use kneadable eraser made by Staedtler. Found at the Lobby for Hobby's. Or other drafting and drawing/art supply stores. Blue stuff at mart store. My teacher wife says blue is the most sticky the yellow and white versions less so 300